The zebrafish is a powerful model organism for the elucidation of molecular mechanisms employed during vertebrate embryogenesis. Initially BMP signaling is activated throughout the embryo but is restricted to ventral domains following the induction of the embryonic shield, the zebrafish equivalent of the Spemann organizer, by maternal Wnt signaling in prospective dorsal marginal cells. Very little is known about the earliest components mediating ventral fate specification during embryogenesis. None of the known mutations affecting BMP signaling mediators including, swirl/bmp2b, somitabun/smad5, snailhouse/bmp7 and Iost-a-fin/alk8 fails to induce the earliest expression of the BMP ligand genes bmp2b, bmp4, bmp7, or the transcription factors vox and vent, required for the inhibition of dorsal fates in ventral domains, strongly supporting the existence of a maternal induction pathway for ventral fate specification. We have identified three dorsalizing maternal-effect mutations. Two of the mutations (18ahub and 10uzat) show recessive maternal-effect inheritance, and the third (Olueai) shows dominant maternal-zygotic inheritance. 18ahub and 10uzat are unique in that there are no recessive dorsalizing maternal-effect mutations described previously, suggesting they may involve novel maternal components of ventral fate specification. The Olueai mutation resembles certain alleles of smadS in its dominant inheritance, penetrance, and expressivity of its phenotype. However, the Olueai mutant yields duplications of tail structures in some embryos, a phenotype distinct from all 8 smadS mutant alleles characterized, suggesting that it may be a mutation in a gene distinct from smadS. I propose to characterize these maternal-effect mutant phenotypes in molecular detail, identify the genes affected, and begin to elucidate the molecular mechanisms by which they act. I will employ in situ hybridization studies of gene expression patterns and epistasis tests with mediators of BMP and Wnt signaling to characterize these mutants relative to known mutants. I will test each of the mutants for linkage to previously characterized mediators of dorsal-ventral patterning and assign each mutation to a chromosomal position using bulk segregant analysis of SSLP markers. I will utilize data from the Sanger Institute's zebrafish genome sequence to determine the molecular nature of each mutation, and subsequently, I will initiate detailed mechanistic studies of these maternal factors in dorsal-ventral patterning of the zebrafish. Mutations affecting several highly conserved components of the Wnt and BMP signaling pathways have been associated with different forms of cancer. Thus, by studying the normal functions of these pathways in embryogenesis I hope to reveal molecular details relevant to the treatment of cancer. [unreadable] [unreadable] [unreadable]